While hinges of the kind that are provided by the invention are not limited to use in orthopedic appliances, they are particularly useful in that connection. It is not uncommon for physicians to prescribe the use of an appliance which includes a means for holding limbs bent at a selected angle at the elbow or wrist or knee. If bending is permitted, the bending may be limited not only in degree but to some particular portion in the range of angular movement. In many instances the physician prescribes that the degree of bending is to be altered with time.
In those cases the appliance is a two-part cast or brace. One part is fixed to the limb below the joint and the other above. The two parts or sections are interconnected with a hinge. Some means is provided for locking the hinge elements at a selected angular degree of hinge opening. While in some prior art designs that angle may be changed by unlocking and relocking the hinge, the degree of change is limited. Hinges that limit angular movement over any segment of a wide range of angles have not been available.
Bending movement at knees and elbows and wrists does not occur about a single pivot point. Cast sections that are joined by a single pivot hinge, with the limb bent at a particular angle, may permit small change in the angle between the cast sections when the pivot axis of the hinge, and of the elbow or knee, are coincident, or nearly so. But when bending of the joint proceeds to a point at which the pivot axes of hinge and joint are no longer aligned, the cast or brace applies forces to limb and joint that can be both intolerably uncomfortable and injurious. In that case the single pivot hinge is entirely inadequate.